What effect has the chewing of tobacco upon the
teeth? 232. What is one reason for preserving health?

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CHAPTER XIII.

THE DIGESTIVE ORGANS.

233. From the earliest existence of the human system to the last ray
of life, change is impressed upon it by the Giver of this curious
fabric. New atoms of matter are deposited, while the old and now
useless particles are constantly removed. The material necessary to
sustain the growth of the body in early life, and also to repair the
waste that is unceasing to animal existence, is the food we eat.

234. Food, animal or vegetable, contains most of the elements of the
different tissues of the system, yet it must undergo certain essential
alterations before it can become a part of the body. The first change
is effected by the action of the _Digestive Organs_.

ANATOMY OF THE DIGESTIVE ORGANS

235. The DIGESTIVE ORGANS are the _Mouth_, _Teeth_,[7] _Sal'i-va-ry
Glands_, _Phar'ynx_, _OE-soph'a-gus_, (gullet,) _Stom'ach_,
_In-tes'tines_, (bowels,) _Lac'te-als_, (milk, or chyle vessels,)
_Tho-rac'ic Duct_, _Liv'er_, and the _Pan'cre-as_, (sweetbread.)

[7] See Chapter XII.

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233. What is impressed upon the human system from its earliest
existence? What maintains this change? 234. Has animal or vegetable
food any resemblance to the different tissues of which it finally
forms a part? By what organs is the first change in the food effected?
235-258. _Give the anatomy of the digestive organs._ 235. Name them.
236. Describe the mouth.

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MOUTH is an irregular cavity, which contains the instruments of
mastication and the organs of taste. It is bounded in front by the
lips; on each side by the internal surface of the cheeks; above, by
the _hard palate_ (roof of the mouth) and teeth of the upper jaw;
below, by the tongue and teeth of the lower jaw; behind, it is
continuous with the pharynx, but is separated from it by a kind of
movable curtain, called the _soft palate_. This may be elevated or
depressed, so as to close the passage or leave it free.

237. The SALIVARY GLANDS are six in number; three on each side of the
jaw. They are called the _pa-rot'id_, the _sub-max'il-la-ry_ and the
_sub-lin'gual_.

[Illustration: Fig. 58. A view of the salivary glands in their proper
situations. 1, The parotid gland. 2, Its duct. 3, The submaxillary gland.
4, Its duct. 5, The sublingual gland, bro